The present invention relates generally to a zoom lens system and more particularly to a compact zoom lens system used with solid-state image sensors, etc.
Size, weight and cost reductions in video cameras are now in drastic progress. In particular, this is true of the size of solid-state image sensors, creating an increasing demand for size reductions in the lens systems used in combination with them.
Some zoom lens systems have been proposed to meet such demand and, of them, a four unit type zoom lens is found to be effective, in which the fourth unit is designed to compensate for an image position during zooming and perform a focusing function as well. Examples of this type of zoom lens system proposed to achieve size and cost reductions are set forth in Japanese Provisional Patent Publication Nos. Hei. 2-39011 and 3-12625. Still, much is left as to size reductions.
In addition, the conventional systems mentioned above cannot be applied directly to a solid-state image sensor of small size, say, about 6 mm or 4 mm in diagonal length, because the associated optical system diminishes in size in proportion to the sensor size, posing some processing problems, for instance, an insufficiency of the peripheral thickness of convex lenses or the central thickness of concave lenses.